The present invention relates to a liquid crystal display for a video monitor such as a television receiver or a display of a computer system, and particularly to a method of fabricating and inspecting the display.
As liquid crystal displays have recently been improved in a low-voltage operation, low power consumption, and thickness, the displays are widely used as AV devices, OA devices, or house-hold appliances as well as television receivers or monitors. Also, they have an increased screen size.
In such a liquid crystal display, a liquid crystal driving LSI is commonly mounted as a semiconductor chip by a mounting method selected from various techniques. As the method, a tape automated bonding (TAB) method and a chip on glass (COG) method are known.
In the TAB method (also called a TAB mounting), a film circuit board (referred to as a tape carrier package or TCP) on which a driving LSI chip is mounted has an output port connected to a liquid crystal panel and an input port connected to an external circuit board. Although the TAB method is often used for a liquid crystal display, an overall size (outline) of the display may significantly increase.
In the COG method (also called a COG mounting), conductors disposed at an edge of a liquid crystal panel are joined directly to input and output ports (called input/output pads) of liquid crystal driving LSIs of a chip form with an anisotropically conductive adhesive. Thereby, the liquid crystal driving LSIs are located about the liquid crystal panel. More specifically, the liquid crystal driving LSI has the output ports connected to a signal line and a scanning line of the liquid crystal panel, and the input ports connected to a terminal conductor provided at a rim (often an outermost end) of the liquid crystal panel.
Signals including a data signal, clock signal, and source voltage for controlling an operation of the driving LSIs are called control signals. In general, the control signals are transferred via each flexible circuit board (also called flexible printed circuit, FPC), which is equipped with transmission lines (also called bus lines), and received by the terminal conductor.
The transmission of the control signals via the FPC to the driving LSIs is more advantageous than along the transmission lines provided on the liquid crystal panel in respect of the resistance in the transmission lines or the availability of the wiring space. This may also be pertinent to a liquid crystal panel of poly-silicon TFT type which has driving circuits provided at the rim of the panel.
The COG method is more favorable than the TAB method in an operation reliability a reducing of an overall product size.
FIG. 14 illustrates a conventional liquid crystal display having driving LSIs mounted by the COG method. The output and input ports of liquid crystal driving LSIs 5, 6 are joined to conductors disposed at the outward edge of a liquid crystal panel 1 with an anisotropically conductive adhesive 9. Flexible circuit boards 101 and 102 are joined to the conductors also with the anisotropically conductive adhesive 9. The flexible circuit boards 101 and 102 has other end connected to corresponding connectors 104 and 105 on an external circuit board 103, respectively. In FIG. 14, the width of the flexible circuit board 101 and the width of the flexible circuit board 102 are denoted by wy1 and wx1 respectively.
FIG. 15 is a schematic overall view of the liquid crystal panel 1. A pixel is disposed at each intersection 2 between a signal line 3 and a scanning line 4. A region of the liquid crystal panel 1 where the pixels are arranged is called an image display region, and the other region where pixels are not disposed is called a non-image display region. The signal line driving LSIs 5 for driving the signal line and the scanning line driving LSIs 6 for driving the scanning line are called driving LSIs. The terminal conductors 7 and 8 (also called connector ports) are disposde at the outward edge of the liquid crystal panel 1. The terminal conductors are classified into signal line terminal conductors and scanning line terminal conductors. The flexible circuit boards 101 and 102 are connected to the signal line terminal conductors and the scanning line terminal conductors, respectively. The circuit board 103, which often employs a printed circuit board, includes a control circuit generating the control signals.
FIG. 16 is a schematic view of a pattern of wiring on the flexible circuit board 101 or 102 and an arrangement of the terminal conductors 208 on the liquid crystal panel 1. As shown in FIG. 16, each flexible circuit board 202 includes transmission lines (bus lines) 200 for transferring the control signals and connector ports 220 corresponding to the terminal conductors 208 joined to the signal line or scanning line driving LSI, respectively. Reference numerals pi1 and pi2 denote the distance between the closest terminal conductors 208 of any two adjacent driving LSIs 206. The distance is called as an LSI pitch hereinafter. Plural driving LSIs are often disposed at various LSI pitchs, respectively.
As shown in FIG. 16, the terminal conductors 210 are connected at least to the input ports of the driving LSI 206. Other terminal conductors may be provided for connecting to a common electrode to which a reference operational voltage is applied, and to a repair line for replacing a defective signal or scanning lines.
In case that the driving LSIs are replaced with different types or their installation is modified due to a specification change in the liquid crystal panel, the LSI pitch or the number of the terminal conductors may be varied. This requires re-designing of the flexible circuit boards.
FIG. 14 illustrates an extended form of the flexible circuit boards 101 and 102. The flexible circuit boards 101 and 102 are often used as shown in FIG. 14 but may be folded to an L-shape or U-shape at the edge of the liquid crystal panel 1 in order to reduce a frame of the liquid crystal display, as not shown.
The flexible circuit boards 101 and 102 are mounted to conductors at the rim of the liquid crystal panel 1 with an anisotropically conductive adhesive 9 which is applied and heated. The board may be heated at a temperature of about 200xc2x0 C. during the heating, as the flexible circuit board is thermally expanded or contracted, the pitch between the connector ports may be deviated from an original one, that is, a pitch error may be developed. If the pitch error is not negligible, the connector ports and the terminal conductors may be connected inadequately. For reducing the pitch error, the pitch between the connector ports may be thermally compensated. The greater the width of the flexible circuit boards (wy1 and wx1 in FIG. 14), the more accurate thermal compensation for the pitch measurements will be required, and thus, the compensation increases an overall cost.
If the liquid crystal panel 1 changes in a specification or screen size, the flexible circuit boards 101 and 102 has to be modified and re-designed (e.g. the overall dimensions). Such a design modification increases a cost significantly because the number of types of the flexible circuit boards has recently been increasing.
The liquid crystal panel 1 is generally inspected, after the driving LSIs are mounted, through a visual examination with a displayed target. If one of the driving LSIs 5 or 6 is found defective, the flexible circuit boards 101 and 102 is dismounted, the defective driving LSI is then replaced by a new one, and the flexible circuit boards 101 and 102 are then mounted again. That raises a cost.
When plural driving LSIs 5, 6 are employed, a data shift signal is transferred through the LSIs in sequence. If a defective driving LSI is included in the LSIs, the data shift signal after the defective driving LSI is not transferred to the succeeding LSIs, which can not thus be inspected. Therefore, the LSIs has to be inspected again after the defective driving LSI is replaced by a new one. That increases a time and cost for manufacturing the display.
A process for removing and replacing the flexible circuit boards or the driving LSIs by new, unused flexible circuit boards or driving LSIs is called as a repairing process.
It is hence an object of the present invention to provide a liquid crystal display and a method of inspecting the display which solve the foregoing problem. The display, for a variety of modifications of the screen size of a liquid crystal panel and of the mounting arrangement, may be designed freely and have a design changed easily especially even for a large sized liquid crystal panel. The display and method allow a defective driving LSI to be specified within a short time, allow the defective driving LSI or flexible circuit board to be repaired or replaced easily, and allow common components to be used. That hence decreases an overall cost and increases an operational reliability.
A liquid crystal display according to the present invention includes a liquid crystal panel, circuit board, and film jumper boards (denoted by FY and FX). The liquid crystal panel includes plural signal lines and scanning lines disposed in matrix, signal line driving LSIs disposed around the lines, first terminal conductors coupled to the signal lines through the signal line driving LSIs, scanning line driving LSIs, and second terminal conductors coupled to the corresponding scanning lines through the scanning line driving LSIs. The circuit board includes connector ports for driving the first and second terminal conductors of the liquid crystal panel. The film jumper boards (denoted by FY and FX) each of which includes control signal lines and dummy lines, is connected to at least one of the first terminal conductors coupled to the signal line driving LSI and the second conductor terminal coupled to the scanning line driving LSI on the liquid crystal panel.
That provides the liquid crystal display which can be easily designed and modified freely, and which has a high operational reliability and a low cost.
The liquid crystal display may include the same number of the signal line driving LSIs as that of the film jumper boards FY which respectively correspond to the signal line driving LSIs. The display may include the same number of the scanning line driving LSIs as that of the film jumper boards FX which respectively correspond to the line scanning LSIs. This allows a defective driving LSI to be repaired easily.
At least one of the film jumper boards FX, FY may include a multi-layer wire for connecting a jumper wire. This allows the film jumper board to have connector ports at one end thereof being fewer than those at the other end.
At least one of the film jumper boards FX and FY may be connected to the circuit board with an anisotropically conductive adhesive by thermocompression-bonding. This contributes to a low cost and a high operational reliability of the liquid crystal display.
The film jumper board FY may be folded from the front side to the back side of the liquid crystal panel along the edge at the end where the first terminal conductors are disposed. The film jumper board FX may be folded from the front side to the back side of the liquid crystal panel along the edge at the end where the second terminal conductors are disposed. Thereby, the liquid crystal display with a narrow frame can be implemented at lower cost.
The film jumper board FY may be connected to the circuit board and the first terminal conductors, and a flexible circuit board may have connector ports at one end connected to the second terminal conductors by thermocompression-bonding, and connector ports at the other end connected to the circuit board with a connector. The film jumper board FX is connected to the circuit board and the second terminal conductors, and a flexible circuit board may have connector ports at one end connected to the first terminal conductors by thermocompression-bonding, and connector ports at the other end connected to the circuit board with a connector. This contributes to the simply assembled construction of the liquid crystal display with a narrow frame.
A liquid crystal display includes a liquid crystal panel, circuit board, and film jumper boards. The liquid crystal panel includes plural signal and scanning lines disposed in matrix, signal line driving LSIs disposed around the lines, first terminal conductors coupled to the signal lines through the signal line driving LSIs, scanning line driving LSIs, and second terminal conductors coupled to the scanning lines through the scanning line driving LSIs. The circuit board includes connector ports for driving the first and second terminal conductors of the liquid crystal panel. The film jumper boards includes control signal lines and connector ports provided at both ends of the control signal lines. Each of the film jumper boards couples the connector ports at one end of the control signal lines with the terminal conductors of at least one of the signal line driving LSIs coupled to the first terminal conductors of the liquid crystal panel and the scanning line driving LSIs coupled to the second terminal conductors of the liquid crystal panel. A method according to the present invention for inspecting the liquid crystal display includes at least one of the steps of- (a) connecting the connector ports at other end of the film jumper board to the transmission lines for the control signals with a connector of the circuit board for the inspection; and (b) connecting between the connector ports at the other end of the film jumper board and the terminal conductors by a pressure for the inspection.
This allows a defective driving LSI or any fault on the film jumper board to be readily specified and correctly repaired fast.
The driving LSIs, if being switched between a cascade operation and single operation, allows a defective LSI to be specified easily.